1. Field of the Invention
The present invention pertains to an impervious shelter made of modules that are placed end to end and communicate with one another.
2. Description of the Prior Art
Prior art shelters of this type have modules in the form of tubes connected end to end. The word "tube" is used in a broad sense to include rectilinear or curved conduits, regardless of their cross section. Each module generally has an outer shell made of reinforced concrete and a solid shell made of sheet metal which covers the inner wall of the concrete shell nearly up to the ends of this concrete shell. The shell made of sheet metal can have its inside lined with a concrete or a cement cover, generally not reinforced and thinner than the outer shell. To make the shelter impervious, the modules have metallic collars at their ends. The collars prolong the shells made of sheet metal. The word "collar" is used in a broad sense which applies even to collars with non-circular sections. These collars are welded on one side to the end of the sheet-metal shell which they prolong and are slightly conical on the opposite side. This conical shape is either a flaring out or a shrinking of the collar. Thus, by associating two collars of these two types together, they can be made to enter each other and provide imperviousness either by means of a seal or through welding. In other examples, the paths of the collars designed to be fitted into one another have substantially constant but different diameters, and the joint is made impervious either by a seal or by welding.
When the collars are welded, the imperviousness of these connections between modules is efficient as regards not only gas, liquids and dust but also electromagnetic waves. However, these connections stand up poorly to the mechanical stresses caused, for example, by earth tremors. These connections then tend to break and thus cause a loss of imperviousness.